The present invention relates to a device for controlling an electrically-operated holding magnet of a parking lock of a motor vehicle, the holding magnet being controlled by the transmission control in which a reset into a basic setting is possible. In addition, the present invention relates to an electrical circuit configuration including a voltage source and an electrically-operated holding magnet, as well as a method for controlling an electrically-operated holding magnet of a parking lock of a motor vehicle transmission, the holding magnet being controlled via a transmission control.
The above-mentioned motor vehicle transmission may be a transmission of any type that is only characterized in that it has a parking lock. Therefore, it is possible, for example, for the transmission to be a double clutch gearbox, in particular a so-called parallel shift gearbox.
The parking lock of such a transmission typically has a parking pawl that is able to block rotation of the transmission output shaft that is connected to the drive train of the vehicle.
At least one transmission actuator, which may also be used to actively engage and disengage the parking pawl, is provided for the gearshift in such a transmission. This transmission actuator requires an operating power, electric power from the vehicle electrical system, for example. In an emergency situation involving a vehicle system voltage failure, the transmission actuator is no longer able to actively engage the parking lock. To correct this problem, it has become known to engage the parking pawl using a spring-type actuator and to disengage it using the transmission actuator. The parking lock operated in such a way may be  held actively disengaged during driving using an electrically-operated holding magnet.
As mentioned above, the solution of using a spring-type actuator to engage the parking pawl has the advantage that the parking lock is also able to be engaged in the event of a power failure. The holding magnet, provided for keeping the parking pawl disengaged, maybe controlled, for example, via the transmission control that may be an electronic control system. Such electronic control systems may be reset to a fixedly-defined basic setting using a reset device. The transmission control is not able to output control signals to the holding magnet during the reset, so that the possibility exists that the holding magnet is not supplied with power during the reset and therefore the parking pawl could become engaged unintentionally during the reset via the spring-type actuator.
Of course, such a reset may also occur during driving of the motor vehicle, e.g., for correcting a fault memory, so that precautions must be taken so that the parking lock is only engaged when this is the driver's intent and is passed on to the magnet by the transmission control, or when the power supply from the vehicle system voltage fails and the parking pawl is to be engaged to avoid accidental rolling away of the vehicle.
The parking lock however must not be engaged when for a short time period no signals are output from the transmission control to the holding magnet, which may be the case in the event of a reset, for example.
U.S. Pat. No. 6,588,294, hereby incorporated by reference herein, shows a parking pawl engaging a gear.